[chunli]

Aldose A is optically active, but treatment with NaBH4 gives alditol B,
which is optically inactive.
Aldose A undergoes Ruff degradation to give Compound C. When
Compound C is treated with NaBH4
, optically inactive alditol D is
formed. However, when C undergoes Ruff degradation, optically active
D-glyceraldehyde is obtained. Give the structures and names of sugars
A–D

[sjb]

Aldose A is optically active, but treatment with NaBH4 gives alditol B,
which is optically inactive.
Aldose A undergoes Ruff degradation to give Compound C. When
Compound C is treated with NaBH4
, optically inactive alditol D is
formed. However, when C undergoes Ruff degradation, optically active
D-glyceraldehyde is obtained. Give the structures and names of sugars
A–D

What does Ruff degradation do to a compound, consider a generic structure, perhaps? What then could C be? If on reduction you get an optically inactive compound, what does that suggest?

[Dan]

For this question, I would work backwards from glyceraldehyde. There are only two sugars that will produce D-glyceraldehyde by Ruff degradation. Apply the chirality information to determine which one it is, this gives you C/D. Then repeat this exercise on C to find A/B.